Method and device for cooling of a superconducting cable and corresponding system

Abstract

The invention relates to a method for cooling a superconducting cable ( 1 ) using a coolant containing or consisting of liquid nitrogen, wherein at least a part of the coolant is subjected to a subcooling step and thereafter brought into thermal contact with the superconducting cable ( 1 ) in a cooling cycle, wherein said subcooling step is at least in part performed using a refrigerant provided in a Brayton process in which at least a part of the refrigerant is cooled and heated in a main heat exchanger ( 11 ). According to the present invention, a part of the coolant is withdrawn from the cooling cycle and heated in the same main heat exchanger ( 11 ) in which at least a part of the refrigerant is cooled and heated in the Brayton process. A corresponding device and a corresponding system are also part of the present invention.

The invention claimed is: 
     
       1. A method for cooling a superconducting cable ( 1 ) using a coolant comprising liquid nitrogen, the method comprising:
 subjecting at least a part of the coolant to a subcooling step and thereafter bringing the at least a part of the coolant into thermal contact with the superconducting cable ( 1 ) in a cooling cycle, 
 wherein said subcooling step is at least in part performed using a refrigerant which is provided in a Brayton process in which at least a part of the refrigerant is cooled and heated in a main heat exchanger ( 11 ) and a part of the coolant is withdrawn from the cooling cycle and heated in the same main heat exchanger ( 11 ) in which at least a part of the refrigerant is cooled and heated in the Brayton process. 
 
     
     
       2. The method according to  claim 1 , wherein the coolant in the cooling cycle is passed through one or more circulation pumps ( 2 ), thereafter subjected to said subcooling, thereafter brought into said thermal contact with the superconducting cable ( 1 ), and thereafter recirculated to the circulation pump ( 2 ). 
     
     
       3. The method according to  claim 2 , wherein said part of the coolant which is withdrawn from the cooling cycle and heated in the main heat exchanger ( 11 ) is:
 (a) withdrawn from the cooling cycle downstream of said thermal contact with the superconducting cable ( 1 ) and before being recirculated to the circulation pump ( 2 ), 
 (b) withdrawn from the cooling cycle downstream of the circulation pump ( 2 ) and before being subjected to said subcooling, or 
 (c) withdrawn from the cooling cycle after a part of said thermal contact with the superconducting cable ( 1 ). 
 
     
     
       4. The method according to  claim 1 , wherein a compander ( 15 ) comprising one or more compression stages and one or more expansion stages is used in the Brayton process. 
     
     
       5. The method according to  claim 4 , wherein the one or more compression stages of the compander ( 15 ) is or are used for compressing at least a part of the refrigerant in the Brayton process, and wherein the one or more expansion stages of the compander ( 15 ) is or are used for expanding at least a part of the refrigerant in the Brayton process or said part of the coolant which is withdrawn from the cooling cycle and heated in the main heat exchanger ( 11 ) or a part thereof. 
     
     
       6. The method according to  claim 4 , wherein one or more further expanders ( 16 ) or expansion stages is or are used to expand
 at least a part of the refrigerant in the Brayton process, or 
 said part of the coolant which is withdrawn from the cooling cycle and heated in the main heat exchanger ( 11 ) or a part thereof. 
 
     
     
       7. The method according to  claim 4 , wherein one or more further expanders ( 16 ) or expansion stages is or are used to expand at least a part of the refrigerant in the Brayton process. 
     
     
       8. The method according to  claim 1 , wherein one or more compressors ( 12 ) or compression stages is or are used to compress at least a part of the refrigerant in the Brayton process, and one or more expanders ( 14 ) or expansion stages is or are used to expand at least a part of the refrigerant in the Brayton process, and wherein the one or more compressors ( 12 ) or compression stages are mechanically coupled to the one or more expanders ( 14 ) or expansion stages. 
     
     
       9. The method according to  claim 1 , wherein a single-shaft compressor ( 17 ) comprising two compression stages is used for compressing at least a part of the refrigerant in the Brayton process. 
     
     
       10. The method according to  claim 1 , wherein said subcooling is performed in a section of the main heat exchanger ( 11 ). 
     
     
       11. The method according to  claim 1 , wherein the coolant contains at least 70% liquid. 
     
     
       12. The method according to  claim 1 , wherein said part of the coolant which is withdrawn from the cooling cycle and heated in the main heat exchanger ( 11 ) is withdrawn from the cooling cycle downstream of said thermal contact with the superconducting cable ( 1 ) and before being recirculated to the circulation pump ( 2 ). 
     
     
       13. The method according to  claim 1 , wherein said part of the coolant which is withdrawn from the cooling cycle and heated in the main heat exchanger ( 11 ) is withdrawn from the cooling cycle downstream of the circulation pump ( 2 ) and before being subjected to said subcooling. 
     
     
       14. The method according to  claim 1 , wherein said part of the coolant which is withdrawn from the cooling cycle and heated in the main heat exchanger ( 11 ) is withdrawn from the cooling cycle after a part of said thermal contact with the superconducting cable ( 1 ). 
     
     
       15. The method according to  claim 1 , wherein said subcooling is performed in a counter-stream heat exchanger ( 11   a ) separate from the main heat exchanger ( 11 ). 
     
     
       16. The method according to  claim 1 , wherein said subcooling is performed in a bath cooler ( 11   b ,  11   c ) separate from the main heat exchanger ( 11 ). 
     
     
       17. A device for cooling a superconducting cable ( 1 ) using a coolant comprising liquid nitrogen, wherein the device comprises:
 a subcooling apparatus for subjecting at least a part of the coolant to a subcooling step before bringing the at least a part of the coolant into thermal contact with the superconducting cable ( 1 ) in a cooling cycle, 
 wherein in the subcooling apparatus includes means for the subcooling, at least in part, a refrigerant in a Brayton process in which at least a part of the refrigerant is cooled and heated in a main heat exchanger ( 11 ), and 
 means for withdrawing at least a part of the coolant from the cooling cycle and to heating the part of the coolant from the cooling cycle it in the same main heat exchanger ( 11 ) in which at least a part of the refrigerant is cooled and heated in the Brayton process. 
 
     
     
       18. A system comprising a device according to  claim 17  and a superconducting cable ( 1 ) arranged to be cooled by the device. 
     
     
       19. The system according to  claim 18 , wherein the superconducting cable is a high-temperature superconducting cable. 
     
     
       20. A method for cooling a superconducting cable ( 1 ) using a coolant comprising liquid nitrogen, the method comprising:
 subjecting at least a part of the coolant to a subcooling step and thereafter bringing the at least a part of the coolant into thermal contact with the superconducting cable ( 1 ) in a cooling cycle, 
 wherein said subcooling step is at least in part performed using a refrigerant which is provided in a Brayton process in which at least a part of the refrigerant is cooled and heated in a main heat exchanger ( 11 ) and a part of the coolant is withdrawn from the cooling cycle, expanded using an expansion valve, and heated in the main heat exchanger ( 11 ) in which at least a part of the refrigerant is cooled and heated in the Brayton process, before being vented to the atmosphere, and 
 wherein the coolant in the cooling cycle is passed through one or more circulation pumps ( 2 ), thereafter subjected to said subcooling, thereafter brought into said thermal contact with the superconducting cable ( 1 ), and thereafter recirculated to the circulation pump ( 2 ), and 
 wherein said part of the coolant which is withdrawn from the cooling cycle and heated in the main heat exchanger ( 11 ) is: 
 (a) withdrawn from the cooling cycle downstream of said thermal contact with the superconducting cable ( 1 ) and before being recirculated to the circulation pump ( 2 ), 
 (b) withdrawn from the cooling cycle downstream of the circulation pump ( 2 ) and before being subjected to said subcooling, or 
 (c) withdrawn from the cooling cycle after a part of said thermal contact with the superconducting cable ( 1 ).